1. Field of the Invention
The present invention relates to a work holder for holding a workpiece, to which a thin film forming method such as sputtering, ion plating or vacuum evaporation is applied, while partially masking the same. More particularly, it relates to a workpiece holder for masking, which is employed for forming a conductor film or a resistor film on a specific part of the surface of a miniature chip-type electronic component such as a chip-type resistor or a chip-type capacitor by a thin film forming technique.
2. Description of the Background Art
In order to obtain a chip-type electronic component such as a chip-type resistor or a chip-type capacitor, for example, a conductor film or a resistor film is formed on a specific part of the surface of a workpiece such as a substrate or a component body. When such a conductor film or resistor film is formed through a thin film forming technique such as sputtering, ion plating or vacuum evaporation, it is necessary to mask a part, which must not be covered with the film, of the workpiece surface. Usually, a single mask is applied to an array comprising a large number of workpieces, and such a mask is usually fixed to a work holder only at its peripheral portion. Hence, an undesirable clearance is inevitably defined between the central portion of the mask and the surface of each workpiece. When such a clearance is undesirably defined between the workpiece surface and the mask, therefore, evaporation particles may enter the clearance, and may spread the film to a region of the workpiece which must not be covered with the film. Therefore, to avoid this problem, it is necessary to bring the mask into close contact with the part of the workpiece surface that is to be masked.
Prior structures for pressing a workpiece against a mask have employed a spring on the work holder, in order to give intimate contact between the workpiece and the mask. However, a work holder for simultaneously holding a large number of miniature workpieces requires such a spring for every workpiece, and hence its structure is complicated. Further, it is not easy to charge (load) the workpieces into such a work holder since the springs must be compressed to define spaces for receiving the workpieces. In addition, the springs are annealed by the heat which is applied in connection with the film forming step and hence their elasticity deteriorates.
On the other hand, an attempt has been made to replace the aforementioned spring by a rubber member, in order to apply a force by the member's elasticity. In general, however, rubber cannot resist a heating temperature of 200.degree. C. in a vacuum state. Hence, such a rubber member cannot resist the environmental temperature of sputtering, for example. Further, rubber evolves gas under a high temperature. Such gas contaminates the film or reduces adhesion between the film and the workpiece.